/*-------------------------------------------------------------------------
 *
 * regexp.c--
 *	  regular expression handling code.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/utils/adt/regexp.c,v 1.20 1998/09/01 04:32:46 momjian Exp $
 *
 *		Alistair Crooks added the code for the regex caching
 *		agc - cached the regular expressions used - there's a good chance
 *		that we'll get a hit, so this saves a compile step for every
 *		attempted match. I haven't actually measured the speed improvement,
 *		but it `looks' a lot quicker visually when watching regression
 *		test output.
 *
 *		agc - incorporated Keith Bostic's Berkeley regex code into
 *		the tree for all ports. To distinguish this regex code from any that
 *		is existent on a platform, I've prepended the string "pg95_" to
 *		the functions regcomp, regerror, regexec and regfree.
 *		Fixed a bug that was originally a typo by me, where `i' was used
 *		instead of `oldest' when compiling regular expressions - benign
 *		results mostly, although occasionally it bit you...
 *
 *
 *-------------------------------------------------------------------------
 */
#include <string.h>
#include "postgres.h"			/* postgres system include file */

#include <regex/regex.h>

#include "utils/builtins.h"		/* where the function declarations go */

#if defined(DISABLE_XOPEN_NLS)
#undef _XOPEN_SOURCE
#endif	 /* DISABLE_XOPEN_NLS */

/* this is the number of cached regular expressions held. */
#ifndef MAX_CACHED_RES
#define MAX_CACHED_RES	32
#endif

/* this structure describes a cached regular expression */
struct cached_re_str
{
	struct varlena *cre_text;	/* pattern as a text* */
	char	   *cre_s;			/* pattern as null-terminated string */
	int			cre_type;		/* compiled-type: extended,icase etc */
	regex_t		cre_re;			/* the compiled regular expression */
	unsigned long cre_lru;		/* lru tag */
};

static int	rec = 0;			/* # of cached re's */
static struct cached_re_str rev[MAX_CACHED_RES];		/* cached re's */
static unsigned long lru;		/* system lru tag */

/* attempt to compile `re' as an re, then match it against text */
/* cflags - flag to regcomp indicates case sensitivity */
static int
RE_compile_and_execute(struct varlena * text_re, char *text, int cflags)
{
	int			oldest;
	int			n;
	int			i;
	char	   *re;
	int			regcomp_result;

	re = textout(text_re);
	/* find a previously compiled regular expression */
	for (i = 0; i < rec; i++)
	{
		if (rev[i].cre_s)
		{
			if (strcmp(rev[i].cre_s, re) == 0)
			{
				if (rev[i].cre_type == cflags)
				{
					rev[i].cre_lru = ++lru;
					pfree(re);
					return (pg95_regexec(&rev[i].cre_re,
										 text, 0,
										 (regmatch_t *) NULL, 0) == 0);
				}
			}
		}
	}



	/* we didn't find it - make room in the cache for it */
	if (rec == MAX_CACHED_RES)
	{
		/* cache is full - find the oldest entry */
		for (oldest = 0, i = 1; i < rec; i++)
		{
			if (rev[i].cre_lru < rev[oldest].cre_lru)
				oldest = i;
		}
	}
	else
		oldest = rec++;

	/* if there was an old re, then de-allocate the space it used */
	if (rev[oldest].cre_s != (char *) NULL)
	{
		for (lru = i = 0; i < rec; i++)
		{
			rev[i].cre_lru =
				(rev[i].cre_lru - rev[oldest].cre_lru) / 2;
			if (rev[i].cre_lru > lru)
				lru = rev[i].cre_lru;
		}
		pg95_regfree(&rev[oldest].cre_re);

		/*
		 * use malloc/free for the cre_s field because the storage has to
		 * persist across transactions
		 */
		free(rev[oldest].cre_s);
	}

	/* compile the re */
	regcomp_result = pg95_regcomp(&rev[oldest].cre_re, re, cflags);
	if (regcomp_result == 0)
	{
		n = strlen(re);

		/*
		 * use malloc/free for the cre_s field because the storage has to
		 * persist across transactions
		 */
		rev[oldest].cre_s = (char *) malloc(n + 1);
		memmove(rev[oldest].cre_s, re, n);
		rev[oldest].cre_s[n] = 0;
		rev[oldest].cre_text = text_re;
		rev[oldest].cre_lru = ++lru;
		rev[oldest].cre_type = cflags;
		pfree(re);
		/* agc - fixed an old typo here */
		return (pg95_regexec(&rev[oldest].cre_re, text, 0,
							 (regmatch_t *) NULL, 0) == 0);
	}
	else
	{
		char		errMsg[1000];

		/* re didn't compile */
		rev[oldest].cre_s = (char *) NULL;
		pg95_regerror(regcomp_result, &rev[oldest].cre_re, errMsg,
					  sizeof(errMsg));
		elog(ERROR, "regcomp failed with error %s", errMsg);
	}

	/* not reached */
	return 0;
}



/*
 *	interface routines called by the function manager
 */

/*
   fixedlen_regexeq:

   a generic fixed length regexp routine
		 s		- the string to match against (not necessarily null-terminated)
		 p		- the pattern
		 charlen   - the length of the string
*/
static bool
fixedlen_regexeq(char *s, struct varlena * p, int charlen, int cflags)
{
	char	   *sterm;
	int			result;

	if (!s || !p)
		return FALSE;

	/* be sure sterm is null-terminated */
	sterm = (char *) palloc(charlen + 1);
	StrNCpy(sterm, s, charlen + 1);

	result = RE_compile_and_execute(p, sterm, cflags);

	pfree(sterm);

	return (bool) result;

}


/*
 *	routines that use the regexp stuff
 */
bool
nameregexeq(NameData *n, struct varlena * p)
{
	if (!n)
		return FALSE;
	return fixedlen_regexeq(n->data, p, NAMEDATALEN, REG_EXTENDED);
}

bool
nameregexne(NameData *s, struct varlena * p)
{
	return !nameregexeq(s, p);
}

bool
textregexeq(struct varlena * s, struct varlena * p)
{
	if (!s)
		return FALSE;
	return fixedlen_regexeq(VARDATA(s), p, VARSIZE(s) - VARHDRSZ, REG_EXTENDED);
}

bool
textregexne(struct varlena * s, struct varlena * p)
{
	return !textregexeq(s, p);
}


/*
*  routines that use the regexp stuff, but ignore the case.
 *	for this, we use the REG_ICASE flag to pg95_regcomp
 */
bool
texticregexeq(struct varlena * s, struct varlena * p)
{
	if (!s)
		return FALSE;
	return (fixedlen_regexeq(VARDATA(s), p, VARSIZE(s) - VARHDRSZ,
							 REG_ICASE | REG_EXTENDED));
}

bool
texticregexne(struct varlena * s, struct varlena * p)
{
	return !texticregexeq(s, p);
}

bool
nameicregexeq(NameData *n, struct varlena * p)
{
	if (!n)
		return FALSE;
	return (fixedlen_regexeq(n->data, p, NAMEDATALEN,
							 REG_ICASE | REG_EXTENDED));
}

bool
nameicregexne(NameData *s, struct varlena * p)
{
	return !nameicregexeq(s, p);
}
